This invention relates to a numerical control apparatus which has a function to repeat a cutting cycle until a work is machined to the final shape indicated in a machining program.
FIG. 1 shows a prior art numerical control apparatus.
In the figure, the reference numeral 1 denotes a machining program; element 2 is a program reading means to read-in the machining program, and element 3 is a final machining shape storing means which stores the final machining shape indicated in the machining program. The reference numeral 4 denotes a cutting start point calculating means to calculate a cutting start point C1 from which cutting starts for each of the plural cutting cycles; element 5 is a cutting start point moving command generating means to generate a cutting start point moving command MV1 to move the tool to the cutting start point C1; element 6 is a rod path line generating means to generate a rod path line B1 based on the cutting start point C1; element 7 is a final machining shape intersection calculating means to calculate intersections of the rod path line B1 and the final machining shape; element 8 is a rod cutting line command generating means to generate a rod cutting line command BV1 to move the tool along the rod cutting line B1 at the cutting rate, and element 9 is a contour cutting line command generating means to generate a contour cutting line command CV1 to move the tool along the contour of the final machining shape at the cutting rate. A cutting cycle controlling means 10 controls the cycle by repeatedly operating the above means 4, 5, 6, 7, 8 and 9 until the contour is machined in accordance with the final machining form, element 11 is a function generating means to generate functions based on the rod cutting line command VB1, the contour cutting line command CV1 and the cutting start point moving command MV1, and a servo controller 12 controls a servo motor in accordance with the generated functions.
The operation of the system will now be described referring to FIG. 2 which shows an example of machining program and FIG. 3 which shows the final machining shape written in the machining program. In the figures, a point S indicates where cutting starts, or the reference point of the cutting cycle.
The program reading means 2 reads in the final machining shape commands "N001"-"N007", and has the data stored in the final machining shape storing means 3. When the program reading means 2 reads in the subsequent cutting cycle execution command "N008", it transfers the cutting cycle execution command C and the cutting cycle start signal CS to the cutting cycle controlling means 10. The cutting cycle controlling means 10 receives as input the cutting cycle execution command C and the start signal CS, and outputs the cutting depth D and the calculation start signal DS to the cutting start point calculating means 4 for calculating the start point. When receiving the cutting depth D and the calculation start signal DS, the cutting start point calculating means 4 receives the current position CPD (in this case, the cutting cycle reference point S) from the function generating means 11, and calculates the cutting start point C1 based on the reference point S and the cutting depth D (refer to FIG. 4), and inputs the cutting start point C1 to the cutting start point moving command generating means 5 to move the tool to the start point and to the rod path line generating means 6. The cutting cycle controlling means 10 transfers the generating start signal MS to the cutting start point moving command generating means 5. The cutting start point moving command generating means 5 generates and outputs the moving command MV1 to move the tool to the cutting start point C1 at a rapid traverse rate after receiving the generating start signal MS. Then, the function generating means 11 generates functions upon receipt of the moving command MV1 to thereby cause axial displacement via the servo motor (see FIG. 4).
The cutting cycle controlling means 10 transfers the generating start signal BS to the rod path line generating means 6. The rod path line generating means 6 generates the rod path line B1 based on the generating start signal BS and the cutting start point C1 (refer to FIG. 5A), and transfers it to the final machining shape intersection calculating means 7 which calculates the intersections with the final machining shape. The cutting cycle controlling means 10 transfers the calculating start signal AS to the final machining shape intersection calculating means 7, which, in turn, judges whether or not the rod path line B1 crosses the final machining shape upon receipt of the calculating start signal AS, and transfers the judgment signal AR to the cutting cycle controlling means 10 as well as transfers the intersection P (refer to FIG. 5B), if they do intersect, to the rod cutting line command generating means 8 and the contour cutting line command generating means 9. When the input judgment signal AR indicates the intersection, the cutting cycle controlling means 10 transfers the cutting feed rate F and the generating start signal BCS to the rod cutting line command generating means 8. The rod cutting line command generating means 8, upon receiving the generating start signal BCS, generates the rod cutting line command BV1 based on the cutting feed rate F, the rod path line B1, and the intersection P (refer to FIG. 5C), and transfers it to the function generating means 11 to generate a function for cutting feed along the rod cutting line as well as to cause axial displacement according thereto (refer to FIG. 4). Then, the cutting cycle controlling means 10 transfers the cutting feed rate F and the generating start signal CCS to the contour cutting line command generating means 9, which in turn generates the contour cutting line command CV1 based on the cutting feed rate F, the intersection P and the final machining shape when receiving the generating start signal CCS (refer to FIG. 5D), inputs the same to the function generating means 11, and generates a function along the final cutting start point moving command generating shape based on the cutting feed rate to cause axial displacement (refer to FIG. 4) accordingly.
The above cutting cycle comprising the axial movements MV1.fwdarw.BV1 .fwdarw.CV1 is repeated by the cutting cycle controlling means 10 until the work is machined to the final machining shape, and as a result, the axial displacement is achieved as MV2 .fwdarw.BV2 .fwdarw.CV2 .fwdarw.MV3 .fwdarw.CV3 .fwdarw.MV4 .fwdarw.BV4 .fwdarw.CV4 .fwdarw.MV5 .fwdarw.BV5 .fwdarw.CV5 .fwdarw.MV6 .fwdarw.BV6 .fwdarw.CV6 as shown in FIG. 4.
In the prior art numerical control apparatus mentioned above, the form of the material work is not considered in generating the cutting line. As a result, as shown in FIG. 6, the program commands the tool to move beyond the limits of the material work where in fact no cutting is needed (idle cutting), to thereby inconveniently prolong the machining time.
In short, the prior art cutting cycle for lathing includes the steps of determining the points along the line segment between the cutting cycle reference point and the point where the contour of the work to be finished starts by dividing the line segment with the cutting depth of the tool and of operating the tool at the cutting rate, starting from each of the above points thus detemined until the tool touches the contour of the work to be finished, whereupon the tool moves along the final contour, cutting the work for its cutting depth. The prior art method is therefore defective in that idle cutting unavoidably occurs when applied to a work of an arbitrary form made by casting or forging, prolonging the machining time.